The invention concerns a system for controlling the locking or unlocking of the differentials in a vehicle, in particular in a truck comprising one or several differentials.
Traditionally, in car or trucks, driving wheels are interconnected and driven thanks to differential(s) in order to authorize a relative speed between driving wheels to allow for instance the vehicle to turn more easily along a curve of the road without loss of adherence and to save fuel consumption.
Depending on the axle and differential set-up of the vehicle, the number of differentials may range from one up to six, or sometimes more.
In some vehicles like four-wheel drive vehicles or in some heavy duty trucks, at least some of the differentials may be locked thanks to corresponding differential locks. The unlocking or locking of each differential is controlled by a dedicated push button or knob having two positions and that can be manually operated by the driver in order to control the corresponding differential lock that locks the differential. Such locking means are very useful in order to cancel relative speed between driving wheels and to avoid loss of drivability when, for instance, one wheel is wheel-slipping.
The use of a push button to lock or unlock each differential is an interface easy to use provided that there are not too many differentials that have to be separately locked or unlocked. In case of many independent differentials, the dashboard could be provided with a lot of push buttons that would cause the driver to take longer time to select a locking configuration of the differentials. Another consequence of such arrangement is that it increases the risk of confusion for the driver and the risk to lock the wrong differential.
To solve these issues, it is known, for example from WO 2009/154553, to use a manually operable switch button that can be rotated around a central axis in order to choose between several locking or unlocking configurations of the differentials.
Such system offers a simplified human interface that is easier to use than several push buttons.
However, a disadvantage of this solution is that the physical position of the switch button is irremediably associated to a locking configuration and so the switch button denotes the status of the locking configuration that is implemented and therefore, a given switch button is irremediably associated to a given axle and differential set-up of the vehicle.
A consequence of such solution is that, in case of numerous differential locking and unlocking configurations, the different positions of the switch button to select one or another configuration can be very close from each other because they have to be spread over a 360° rotation, so that it increases the risk for the user to select the wrong configuration.
Furthermore, this switch button is dedicated to one axle and differential set-up and it can't be easily modified so that it can't be easily used with another vehicle having a different axle set-up.
A further disadvantage of the system disclosed in WO 2009/154553 occurs when the driver decides to rotate the switch button in order to lock one or several differential because when he does it, he also has to visually match the position of the switch button with an indicator that corresponds to the chosen configuration. Therefore, if the control member is not positioned within the viewing field of the driver, the driver has to look away from the road or to stop the vehicle to lock a differential.
It therefore appears that, from several standpoints, there is room for improvement in systems that allow to control locking/unlocking positions of differentials in a vehicle.
In this technical context, an object of the invention is to improve the system for controlling the locking or unlocking positions of differentials which can overcome the drawbacks of the prior art systems.
To this end an aspect of the invention concerns a differential control system for a motor vehicle having driving wheels, drive shafts to transmit driving power from the motor to the driving wheels and at least one differential to interconnect drive shafts.
The differential control system comprises:                at least one differential lock which is able to operate the differential into at least a locked or an unlocked state,        a controller that controls the differential lock,        a manually operable control member freely rotating bidirectionally around at least one axis,        an encoder connected to the control member to convert a rotation of the control member into a signal fed to the controller which controls' the differential lock in order to operate the differential into at least a locked or an unlocked state.        
Depending on the type of differential lock, it is also possible to operate, the differential into intermediate states between a fully locked and a fully unlocked state.
The adverb “freely” means that the angular position of the control member doesn't assign by itself a locked or unlocked state, or doesn't assign a locking configuration as defined hereafter. That also means that the control member has no angular end position and may be operated on several complete rotations around the rotation axis.
The encoder may be located between the control member and the controller, or it may be integrated into the control member or into the controller.
The invention also concerns according to an aspect thereof motor vehicles having at least two differentials, in such case the differential control system may comprise several differential locks controlled by the controller in order to operate the differentials into different locking configurations where each differential can be operated into at least a locked or an unlocked state.
According to an aspect of the invention, it is understood that for the same locking configuration one or some differentials can be operated in a locked state whereas one or some other differentials can be operated in an unlocked state. It is also understood that a locking configuration may also be a configuration where all the differentials are unlocked.
The fact that the control member can freely rotate and therefore has no predefined position in relation to a locked or unlocked state or to a locking configuration makes it possible to disconnect the actual position of the control member from the current locking configuration. Thus, a locking configuration is not bound by a position of the control member, unlike with a conventional switch wherein the position of the switch sets the vehicle differential locking configuration.
Unlike prior differential control system wherein a control member rotates adjacent to a series of reference numbers that indicate the differential locking configuration, that is implemented, the inventive control system doesn't rely the angular position of the control member to implement a given locking configuration. Consequently, there is no need to use reference numbers or any other indicator to mark the angular position of the control member according to the invention. Another advantage of the present invention is that the driver no longer needs to visually check the position of the control member. Operation of the inventive control system proves to be significantly easier and more user friendly than conventional system.
A further advantage is that the same control member can be used in different vehicles having different axle and differential set-ups. For the vehicle manufacturer, the possibility to assemble the same component or spare part in different vehicles is a great advantage for the supply chain.
Another advantage is that selection of the different locking configurations of the differentials can be spread over a range of rotation of the control member that is not limited to 360°.
According to advantageous but optional features, considered on their own or in any technically feasible combination:
In a preferred aspect of the invention, the control member, the encoder and, the controller are configured so that a manual rotation of the control member allows to select one locking configuration and a further rotation of the control member to select a new locking configuration.
In the present invention, the controller implement a new configuration depending on an electric or electronic signal received from the encoder and which preferably corresponds to the angular amplitude of a manual rotation of the control member.
In an embodiment of the invention the control member, the encoder and the controller are configured so that a new locked/unlocked state or new locking configuration could be implemented only if the rotation of the control member exceeds a predetermined angular amplitude threshold.
Such an angular amplitude threshold is preferably determined before the motor vehicle is used by the end user and may be determined by the vehicle manufacturer itself. Such a predetermined angular amplitude threshold may be comprised between 10 and 180° and preferably between 30 and 60°.
It can be envisaged that the predetermined threshold angular amplitude is different depending on the new locking configuration that is selected.
In another embodiment of the invention the controller is configured to authorize the implementation of a new locking configuration only after a predetermined period of time following the selection of the previous locking configuration.
Such a predetermined period is preferably determined before that the vehicle is used by the end user, it may be determined by the vehicle manufacturer itself and may be comprised between 1 and 5 seconds.
In a further embodiment of the invention the control member, the encoder and the controller are configured so that a new locking configuration can be implemented only if the control member is rotated at a rotation speed which is lower than a predetermined speed threshold.
Such a predetermined speed threshold is preferably determined before that the vehicle is used by the end user, it may be determined by the vehicle manufacturer itself and may be comprised between 1 rad/s and 6 rad/s.
In a preferred aspect of the invention, the rotation of the control member in one direction allows to increment locking configurations and the rotation of the control member in the other direction allows to decrement locking configurations.
In another preferred aspect of the invention, the differential control system is able to operate in an automatic mode. In this case the controller controls the differential locks in order to modify the locking configuration regardless of the current angular position of the control member.
It can be envisaged that, in the automatic mode, the controller is configured to refuse the implementation of a new locking configuration depending on at least one vehicle parameter and/or road condition parameter and/or weather condition parameter.
In particular the controller can be configured to refuse the implementation of a new locking configuration if it can't be operated in a safety manner.
The vehicle parameter may at least comprise the speed of the vehicle and the controller may refuse to implement a new configuration if the speed of the vehicle is above a speed threshold. Such a speed threshold may be determined by the vehicle manufacturer itself and/or may be modified after by a professional who is authorized.
It can also be envisaged that, in the automatic mode, the controller is able to automatically operate a new locking configuration depending on at least one vehicle parameter and/or road condition parameter and/or weather condition parameter.
The vehicle parameter may comprise at least the speed of the vehicle and the controller may automatically unlock at least one differential when the speed of the vehicle reaches a speed threshold. This new predetermined speed threshold can be the same than the preceding one (about 30 km/h) or may be different and the controller preferably unlocks all the differentials when the speed of the vehicle reaches the speed threshold.
In another embodiment of the invention the differential control system also comprises rotation speed sensors located in the vehicle in order to measure the speed of each driving wheel. Rotation speed sensors transmits speed data to a CPU (Central Processing Unit) which compares rotation speeds of the driving wheels to determine a relative speed between opposite driving wheels. In this case the controller is configured to lock at least one differential when the relative speed between the corresponding driving wheels exceeds a predetermined rotation speed threshold.
The CPU could be a dedicated one that is independent from the controller or could be the CPU of the controller.
The predetermined rotation speed threshold is preferably determined before the motor vehicle is used by the end user, it may be determined by the vehicle manufacturer itself.
In a motor vehicle that also comprises a main electrical circuit, it can also be envisaged that, in an automatic mode, the controller is configured to implement a default configuration when the main circuit is turned OFF or when the motor is restarted after that the main circuit has been turned OFF. The default configuration may be a configuration where for instance all the differentials are in an unlocked state.
Preferably, in the automatic mode, the controller is configured to maintain a current locking configuration for a preset period of time when the main circuit is turned OFF and then when the main circuit is turned ON after said preset period of time the controller controls the differential locks in a default configuration where for instance all the differentials may be operated in an unlocked state.
It can be envisaged that the differential control system also comprises a second control member which is manually operable. This second control member may be located in the center of the first control member and may be movable according to different directions than the first control member. An actuation of the second control member may allow to command a further function of the system.
In a particular embodiment of the invention, the second control member is connected to the controller in such a way that a manual action on it implements a default configuration. The default configuration may be a configuration where for instance all the differentials are in an unlocked state.
In another particular embodiment, the second control member is connected to the first control member so that a manual action on the second control member locks in rotation the first control member.
The differential control system according to any one of the preceding characterized in that it also comprises a display device to inform the driver about the locking or unlocking state of each differential.